1. Field of the Invention
This invention relates to filtration and more particularly to the enhancing of filtration by electrical action.
The design of a filter to remove particles from a fluid must be a compromise between the obstruction the filter produces in the desired flow of the fluid and the efficiency of removal of particles from the fluid. It is known that in certain circumstances the action of a filter can be enhanced by the application of an electric field. An enhanced filter might for example offer less obstruction for a given removal of particles than the unenhanced version. Clearly the choice of parameter enhanced in any given filter, subject to design constraints, can be a matter of choice.
The way in which electrical action enhances filter action is believed to be understood for certain distinct classes of filter and electrical action.
2. Description of the Related Art
One very important filter is the deep-bed filter in which the spaces are large compared with the size of the particles to be filtered and the filter medium is relatively loosely packed. The pore volume can be 20 to 30% or even more. A significant use of deep-bed filters is depth filtration for drinking water supplies. In this a relatively deep layer or bed of filter medium, such as sand, is used to adsorb particles on the surface of the medium with minimal pressure loss in the passage of the water through the relatively open filter. While such a filter is effective in removing many of the particles small particles tend to follow the hydraulic streamlines and pass through the filter medium.